The goal of this research program is to understand the neurobiology of early learning. To date, large metabolic, morphological and neurophysiological changes have been described as a consequence of such learning. In the proposed research, we will investigate the mechanism for a striking increase in the number of cells in the region of the rat olfactory bulb that is involved in the processing of the learned odor. Five alternative hypotheses are described to account for the increase in cell number as a function of early learning. An increase in cell production, a decrease in cell death, and a change in the patterns of cells migration are possibilities that will be evaluated by differential labelling of dividing cells after different time periods during development. An increase in the size of the dendritic arbors that may attract an increased number of migrating cells will be determined with the use of vital dyes. Finally, an increase in the concentration of the radial glia, on which the neural population migrates, or an increase in a focal astrocyte population will be determined with immunohistological techniques. All of these techniques will be combined with a technique to isolate focal regions of increased metabolic activity that are characteristic of different olfactory cues. In these ways we hope to identify the mechanism that underlies the reorganization of olfactory bulb circuitry during early life.